This invention relates to an on-board solid carbon dioxide or dry ice refrigeration system for rail (railroad) cars and more particularly to the construction and methods of use of the dry ice bunker, the freight storage compartment and the divider between the two when utilizing carbon dioxide as an expendable refrigerant in transporting products by railroad cars but also useful for other substantially sized vehicles such as trucks, trailers, shipping containers and the like being moved over substantial distances or in circumstances where enroute cold temperature protection is essential, and in an arrangement where no mechanical refrigeration device is included, principally using, as appropriate to each specific case, bunker construction and placement, bunker filling method, bunker vent size and inlet ducting, as well as convectors (and location of each), natural phenomena, cargo area construction and insulation choice and techniques to maintain the cargo in the refrigerated state, and especially useful to food cargo in the frozen state.